J. Sauber, S. Luthcke, S-Ch Han, D. Hall, ( NASA GSFC) Collaborators:

1. Measurement and Modeling of Cryosphere‐Geosphere Interactions • J. Sauber, S. Luthcke, S-Ch Han, D. Hall, (NASA GSFC) Collaborators: R. Bruhn, R. Forster, M. Cotton, E. Burgess, J. Turrin (U of Utah) • B. Molnia, K. Angeli and ASC staff (USGS) N. Ruppert (UAF, AEIS), R. Muskett, C. Lingle (UAF) • R. King, T. Herring (MIT), S. McClusky (ANU)

2. Campaign GPS ISLE GRACE Terra ISLE AB35 DON GPS AB35 PBO GPS • Cryosphere-Geosphere signals in campaign and PBO GPS observations • Cryosphere change from GRACE • Post-1964 earthquake gravity change & ice mass change trends GRACE processing of L1B data: PyLith & other numerical models MacBook Air Dual Core Mac Desktop 6 Cores Mac Cluster ~50 cores DISCOVER (GSFC HEC) Use ~150 cores

3. The GPS station positions for both sites are predicted to move to the north-northwest (NNW) and up due to (steady) tectonic forcing (PCFC relative NOAM) • 1993-1995 surge interval versus post-surge time period, 1996-2001: • A higher uplift rate for ISLE. Site is moving faster to the northwest. Ice unloading to the south of the site would cause uplift & north directed motion. • In contrast, the station DON is undergoing vertical subsidence during the surge but uplift subsequently (as predicted for tectonic loading). The rate of the northward motion is lower during the surge. Sauber and Molnia, 2004

4. 1993-1995 Bering Glacier Surge: A Solid Earth Geophysicist View Represent 10s of meters of drawdown(unloading) in surge reservoir and thickening & terminus advancement in receiving/terminus (loading) region as disc loads Surge Related Predicted Horizontal Displ. N: 7 mm E:4 mm As a “local load”, use elastic half-space model or radially stratified, gravitating Earth model to predict vertical and horizontal displacements [Farrell, 1972]. Elliott et al.,2013 estimates of horizontal site velocities between 2005-2008: DON: ~43 mm/yr @N30oW ISLE: ~20 mm/yr @N14oW N: 12 mm E: -5.5 ISLE Assumptions& Limitations in predicted values: 1993-1995 net transfer of ice mass from surge reservoir to receiving area over the duration of surge is equal (~14km3). GPS motions reflect magnitude of (un)loading & can be used to invert for process scaling factor. Ignores seasonal snow/ice build-up & summer melting. Horizontal component is complex due to tectonic strain as well as possible push moraine toward DON due to surge . Predicted Vertical Displ. reservoir ISLE 38 mm uplift receiving DON DON -42 mm Sauber et al., 2000

5. Surge dynamics on Bering Glacier, Alaska, in 2008–2011 E.W. Burgess , R. R. Forster , C. F. Larsen , and M. Braun, Cryosphere, 2012 2008-2011 was a smaller surge than 1993-1995, with less terminus advancement Below: L-, C- and X-band SAR derived ice horizontal displacement rate (m/day) via offset/speckle tracking methods along a longitudinal profile of the Bering Glacier reservoir receiving Above: Repeated aircraft laser altimetry of elevation change (m/yr) GPS PBO observations in this area began ~ 2007

6. MONTHLY Mean Land Surface Temperature (LST) from Terra MODIS (11.02 and 12.02 mm) March 2005 -4 to -1 -1 to 0 0 to 1 1 to 2 2 to 3 > 3oC March 2012 AB35 AC09 AB42 Melt onset Sauber et al., AGU, 2013

7. North East AB42 AC09 Up AB32 • Similar rates of horizontal deformation at the 3 coastalGoAsites . • Uplift rates are more variable. (SOPAC GPS Explorer combined solution)

8. Detrended North, East and Up for AB42, AB35, and AC09 (SOPAC, GPS Explorer) Up annual term (mm): AB42: 12.9 + 0.1 AB35 = 10.5 + 0.1 AC09 = 7.9 + 0.1

9. GPS multipath for snow depth estimation (K. Larson & colleagues): AC09 Up to almost a meter of snow near AC09. In this marine environment the snow has high water content and undergoes compaction as the season progresses. Snow loading begins ~Mid-September to October and reaches a maximum in late Feb-March. 1 km (hydrologist) versus 10 km (geophysicist) versus regional estimates.

10. CIG Pylith finite element model: --Single 10km load at (0,0) with time history given by AC09 snow profile & r= 1. --20 km elastic layer over 80 km Maxwell viscoelastic layer meters meters Solid Earth response to Snow Loading March April November 90 days No of days*10

11. May 2005 -4 to -1 -1 to 0 0 to 1 1 to 2 2 to 3 > 3oC -4 to -1 -1 to 0 0 to 1 1 to 2 2 to 3 > 3 May 2012 May 2012 AB35 AC09 AB42 Snow mostly gone

12. GRACE estimates of mass change • 41,168 equal area 1-arc-degree mascons are directly estimated from GRACE KBRR L1B data from the GRACE project [Tapley et al., 2004] with spatial and temporal exponential taper constraints applied. • 10-day temporal resolution • Spatial constraint: 100 km correlation distance • Temporal constraint: 10-day correlation • Includes: LIA (Larsen et al., 2005) • and ICE5G(Peltier, 2004) corrections Gulf of Alaska mascons (61) Overall G of Alaska Trend = -69 ± 11 Gt a-1 but note variability from year to year such as the cold (2012) versus warm water (2005) years. Gt GSFC Mascon solution, Luthcke et al., J. of Glaciology, 2013

13. * NC Regional Variability: * Mascon 1425, South Eastern Alaska: Large seasonal, up to 100 cm w.e. (p to p) Small 10 year-trend in ice mass loss Gulf of Alaska SE Mascon 1457: Central Coastal (study area) Moderate seasonal, 50 -75 cm w.e. Largest 10-year trend * 1484 cm w.e. Mascon 1484: North Central Smaller seasonal signal Moderate 10-year trend 1425 1457 Year

14. GRACE MASCONS near three cGPS sites 1449 (AB42) cm w.e. 1457 (AC09) 1456 AB35) Reminder: GRACE is sensitive to changes at spatial scales >300km NEXT SLIDE: We use the estimate of the temporal history of mass change to estimate surface load changes again assuming a 10km load near a site.

15. CIG Pylith finite element model: --Single 10km load at (0,0) with time history ((cm w.e. profile) given by GRACE water year 2012 --20 km elastic layer over 80 km Maxwell viscoelastic layer November August - September. February Days x 30

16. Simulation of the present-day postseismic gravity change 1964 Mw = 9.2 Prince William Sound (Alaska) earthquake Postseismic gravity change in EWH [cm/yr] Spherical harmonic coefficients from RL05 CSR L2 monthly data, degree up to 60; ~330 km resolution. => ~1 cm/yr of gravity change (in w.e.) is predicted, primarily dependent on the asthenosphere viscosity (1019 Pa s) ~1 cm/yr Schematic Epicenter of the 1964 Alaska earthquake • Used Johnson et al. [1996] finite fault model: inversion of tsunami and geodetic data to estimate 1964 coseismic slip • We used the viscoelastic Earth model that is consistent with other studies in this region [Suito and Freymueller, 2009; Sato et al., 2010] • Global normal mode relaxation code was used to compute the gravity change over the period 2002 - 2014. (Courtesy of R. Riva and F. Pollitz)

17. Time-series at the epicenter (60N 212W) The postseismic gravity change could be as large as 10% of the observed mass change, even 50 years after the 1964 earthquake. GRACE secular trend ~ –8.3 cm/yr (observed RL05 CSR L2 ) 1964 EQ postseismic change ~ +1.0 cm/yr (model predicted)

18. Summary How does cryosphere mass change on times scales of months to years in southern Alaska? The individual GRACE mascons located in distinctly different regions capture important inter-annual variations in the magnitude of the seasonal signal wastage trend. These GRACE differences are important for estimating the timing and magnitude of broad-scale differences between regional GPS sites; however, more local estimates of changes in snow/ice extent and magnitude are needed to model cryosphere signal in GPS time series. As estimated from EarthScope GPS data and FEM modeling, how do the surface displacements due to inter-annual and seasonal cryosphere mass change compare to tectonic displacement rates? In the study region the surface horizontal displacements due cryosphere changes are generally <10% of the tectonic displacements whereas the vertical displacements can be comparable in magnitude to predicted tectonic uplift rates in localized regions near glaciers. With a longer history of continuous GPS, and careful management of the sites, we may be able to use GPS derived changes in vertical and horizontal displacements to constrain process oriented models of cryospherechanges.